A new type of electron tube has evolved over the last two decades called the Orotron, Ledatron or Diffraction Radiation Generator. The tube generally consists of an electron beam generator and collector and a Fabry-Perot cavity containing one grooved metallic mirror or grating and one smooth metallic mirror. The principle of operation of these devices is based on the Smith-Purcell effect or Salisbury effect. These devices generate electromagnetic radiation and are made tunable by either changing the electron beam voltage and/or by relative mechanical displacement of the metal mirrors.
Exemplary of such devices is that disclosed in U.S. Pat. No. 2,634,372 to Salisbury. The device of the patent comprises generally an electron gun which directs an electron beam into a region generally adjacent a metallic diffraction grating. An opposed metallic reflecting mirror cooperates with the diffraction grating to establish a standing electromagnetic wave. The electron beam passing through the standing wave increases the amplitude of the standing wave pattern, thus increasing the energy contained in the standing wave. The energy produced may be taken off through an output means. In order to control the frequency of the generated radiation the angle between the reflecting mirror and the diffraction grating must be adjusted. This requires a somewhat complex structure and precise control over the position of the movable reflector.
Another drawback of the prior art devices is that at very high frequencies metal conduction losses can become severe so as to lower the Q of an open resonator. This can become quite severe for wavelengths of approximately one millimeter or less. This reduction in Q lowers the efficiency of the generator.
Accordingly, it is an object of the invention to provide means to improve the efficiency of an open resonator structure such that the radiation generator may operate efficiently at sub-millimeter wavelengths.
It is an object of the invention to construct an electromagnetic wave generator having few metallic parts, thereby improving the cavity Q, thus enabling the generator to operate at higher efficiencies.
It is another object of the invention to provide an electromagnetic wave generator which may be tuned without the use of complex and costly positional adjustment means for the reflecting surfaces.
It is a further object of this invention to improve the spectral purity of the radiation generated by the wave generator.